BiFeO3晶体价键电子结构与铁电性质的关系

通过价键电子理论工具,计算得到了钙钛矿型单相多铁材料BiFcO₃"赝立方"顺电相和斜方铁电相价键电子结构,分析了价键电子结构变化时其铁电性的影响.计算结果表明,从顺电相到铁电相,BiFeO₃晶胞中各类化学键的键长和价键电子数变化各异,其中Bi-O键键长变短,价键电子数增多,共价性显著增强,对铁电相的稳定起到至关重要的作用;Fe-O键长呈现变大和变小两种结果,价键电子数都减小,共价性减弱.计算结果与第一性原理计算进行了比较.

Relationship between valence-bond electronic structure and the ferroelectricity of BiFeO3

By using the method of valence-bond electronic theory, the valence-bond electronic structures of pseudo-cubic phase and actual rhombohedral phase of BiFeO3 are presented. The affection of valence-bond electronic structure on the ferroelectricity of BiFeO3 is analyzed. The theoretical result shows that the different kinds of chemical bond have different bond lengths and bond electron numbers when the crystal transits from paraelectric phase to ferroelectric phase. The Bi-O bond becomes shorter and the bond electron number turns to be larger, which makes the covalent character of Bi-O bond enhanced and is the key factor of stabilizing the ferroelectricity. At the same time, the Fe-O bond shows two kinds of changing results, decrease and increase, respectively. Both of those bond electron numbers are reduced, which indicate that the bond character of Fe-O is of less covalence. Comparison is also made with the corresponding theoretical calculation results of the first-principle.